Electrical stress-directed evolution of biocatalysts community sampled from a sodic-saline soil for microbial fuel cells

Anode-respiring bacteria (ARB) perform an unusual form of respiration in which their electron acceptor is a solid anode. The focus of this study was to characterize the electrical stress direct evolution of biocatalysts as a way of enriching the community with ARB for microbial fuel cell. The original microbial consortium was sampled from a sodic-saline bottom soil (Texcoco Lake). Interestingly iron (III) reducing bacteria consortium in the sodic-saline bottom soil was 8500 ± 15 MPN/100 mL by the most probable number method, since microbial reduction of iron (III) is reported to be associated to anode-respiring capabilities. Cyclic voltammetry studies of electrochemical stressed biofilm-ARB were conducted at 28 ^th and 135 ^th days, and an irreversible electron transfer reaction was found possibly related to electron transfer reaction of the cytochrome. The electrochemical impedance spectroscopy results revealed that the resistance of the biofilm-ARB decreased with time (28 ^th day-11.11Ω and 135 ^th day- 5.5Ω), possibly associated to the adaptability of electroactive biofilm on the graphite electrode surface. Confocal microscopy showed that the biofilms are active in nature and the biofilm-ARB attained ∼40 μm thickness at the 136 ^th day. Electrical stressed-ARB gave a maximum power density of 79.4mW/m ², and unstressed-ARB gave a maximum power density of 41.0mW/m ² in a single-chamber microbial fuel cell (SCMFC). All these electrochemical experiments and evaluation suggest that the electrical-stress directed evolution of ARB community was associated to a more efficient extracellular electron transfer process in SCMFC.